Switch blade construction



April 15, 1958 J. J. KUESER 2,831,090

SWITCH BLADE CONSTRUCTION Filed April 29, 1957 .lllll?" /NVEN7'OR:

ATTORNEYS.

United States Patent SWITCH BLADE CONSTRUCTION John Joseph Kueser, St.Louis, Mo., assignor to Knapp- Monarch Company, St. Louis, Mo., acorporation of Missouri Application April 29, 1957, Serial No. 655,678

4 Claims. (Cl. 2llll138) This invention relates to an improvement in theconstruction of sheet metal switch blades, and more particularly toswitch blades which carry insulator studs adapted to be engaged toeffect movement of the switch blade which carries the insulator stud.

The use of resilient sheet metal switch blades which carry insulatorstuds, or pins, adapted to be engaged by another member, such as abimetal of a thermostatically controlled switch, to etfect movement ofthe switch blade is, of course, notoriously old. However, the means ofsecuring the insulator pin or stud to the sheet metal switch blade hasposed a ditllcult problem for many years.

It is essential that the insulator stud be secured firmly to the sheetmetal switch blade so as to avoid any tendency to become loose, orwobble, or tilt, as such action may interfere with the proper operationand calibration of the thermostatically operated switch of which theswitch blade is a part thereof. Once the thermostatically controlledswitch has been properly calibrated at the factory, any looseness ortilting of the insulator pin thereafter will bring about improperoperation of the switch. 7

Numerous attempts have been made to solve this problem, and heretoforethe best practical solution devised included cementing the stud to theswitch blade with special cements. The latter solution, while ofconsiderable use and success, nevertheless still has its failings inthat after considerable usage, or even when new if the cement has notbeen properly cured, the cement cracks and the studs fall out of placeso that the thermostat then doesnt work at all. p

The object of the instant invention is to provide a novel switch bladeconstruction carrying an insulator stud which is constructed that anytendency of the insulator stud to become loose or fall off the switchblade is, to all intents and purposes, completely eliminated.

In the instant invention, the switch blade is formed to define astud-receiving hole and a collar, of resilient material formed from theswitch blade, surrounding the hole, and a hard ceramic insulator pin ispress fit into the hole and collar so that the material of the collarfrictionally engages the pin to hold the pin in position.

Further objects and advantages of this invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize this invention will be pointed out with particularity inthe claims annexed to and forming part of this specification.

A preferred embodiment of the invention is shown in the accompanyingdrawings, in which:

Figure l is a cross-section view through a typical switch assemblyshowing a switch blade thereof constructed in accordance with thisinvention;

Figure 2 is a top plan view of the switch of Figure 1;

Figure 3 is a fragmentary detail view of the assembly of the ceramic pinin the switch blade; and

Figure 3a is a fragmentary detail similar to Figure 3 Patented Apr. 15,1958 illustrating a typical failure of material that occurs when thecollar on the switch blade is formed of a length beyond the criticallimits disclosed herein.

Referring now to the drawings, there is shown in Figures 1 and 2 atypical switch construction 10 which includes the improvement of thisinvention. So that the entire device shown will be understood, it isnoted that the typical switch construction 10 includes a stackedarrangement of parts which comprises switch blades 12 and 14 thatrespectively carry contacts 16 and 18. The switch blades are carried onan annular block insulator 20, and said blades 12 and 14 arerespectively in electrical contact with connector plates 22 and 24.Appropriate mica insulating washers 26 are provided. There is alsoprovided a mounting plate 28 and a bifurcated spring member 30, and theentire assembly is connected by means of an eyelet 32, the ends of whichare spun over to clamp the parts together.

The mounting plate 28 carries an adjusting screw 34 having an insulatedtip 36 for engagement with the switch blade 14, so as to control theposition of the blade 14 relative to the switch blade 12. The bifurcatedspring 39 cooperates with the head of the adjusting screw 34 to preventthe screw 34 from working loose. The switch blade 12 is provided with acentral aperture 38 through which the adjusting screw 34 extends, as iswell known in the art.

The switch blade 12 is normally biased toward blade 14 and is of greaterlength than the switch blade 14, as seen in Figure l. The extended endof switch blade 12 carries therein an insulator pin, or stud, 40 whichis adapted to be engaged by a thermostatically controlled member such asa bimetal (not shown), to effect separating of the contacts 16' and 18,in a manner well known in the art.

The instant invention is directed to the manner in which the insulatorstud 40 is connected to the switch blade 12. The switch blade 12 ispunched, or otherwise appropriately formed, so as to define a hole 42therethrough in which the insulator stud 40 is mounted. In the formingof the hole 42 the material which immediately surrounds the hole 42 isextruded and formed to define a collar 44, and the annular edge 46 whichwould normally surround and define the hole 42 is displaced from theplane of the main portion of the switch blade 12 so that said edge 46 isdisposed in a plane spaced from, and substantially parallel to, theplane of the main portion of the switch blade 12.

The insulator stud 40 is an elongated member formed of an appropriateceramic, and is arranged to be force fit through the circular opening42' in the switch blade. The stud 441 is of such a size relative to hole42 and collar 44 that it frictionally engages a circumferential, innerperipheral portion 48 of the collar 44, so as to elfect a permanentresilient gripping of the ceramic stud t-i'l by the material of thecollar 44.

The formation of the collar 44 is very critical in that if the collar 44is of too short an axial length, the edge as is disposed converginglytoward the plane of the main portion of the switch blade 12 and thusprovides a sharp edge which, when in contact with the ceramic pin 4t mayimpress such great stresses on the pin 40 as to effectcompression-failure of the ceramic. If the collar 44 is formed of toogreat a length, then it may be stretched beyond its elastic limit sothat the driving of the pin 49 through the hole 42 into frictionalengagement with the collar 44 may produce sufficient stresses on collar44 to effect structural failure of the collar 44, such as by tearing soas to produce a fissure, as shown at fill in Figure 3a.

It has been determined that the length of the collar 44 should beso'selected that the terminus 46 of collar 44 is spaced from the switchblade 12 a distance of from two or four times the thickness of thematerial of the switch blade, and preferably said terminus 46 should bespaced from the switch blade 12 a distance in the range of three timesthe thickness of the material of said switch blade.

The foregoing critical limits have been determined particularly for usewith a switch blade wherein the average thickness of the blade was .012inches. it was determined that the spacing of terminus 46 from theswitch blade 12 should be in the range of .024 to .048 inches, with apreferable average spacing of .036 inches. A switch blade of this typewas formed of a high content nickel stainless steel known commerciallyas Permanickel, having a bright finish, being fully hardened and springtempered, but not age hardened, and having a hardness rating of RockwellC 30/40. Said material has a yield strength of about 120,000 pounds persquare inch and has a 15% elongation. In the manufacture of the switchblade 12, after it is stamped and formed, it is stress relieved byheating to 500 F. for one one hour, during which time the blade 12 mustbe free of load. Thereafter the blade is cooled in air, and laterpickled and bright dipped.

The type of ceramic that may be used in constructing the insulator stud40 may, for example, be a steatite which is fired to a dense structurethroughout, and a typical commercial form is referred to as Alsimag #35,having a ball mill finish so that the entire surface is a smooth finishthroughout. It is important that stud 40 be of very hard ceramicconstruction.

The arrangement of the ceramic pin and the collar 44 is such that whenthe ceramic pin extends through the collar 44 the pin is forced intoengagement with an annular band portion 48 of the collar, which portioniii has some axial length thereby increasing the area of contact betweenpin 40 and collar 44, so that the compressive force exerted by thecollar is distributed over a relatively large area wherein the pin 40 isin contact with the collar so as to distribute the compressive force andto avoid compression-failure of the ceramic.

While there has been shown and described a particular embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made therein without departing from theinvention and, therefore, it is intended in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is:

1. A bimetal-operated switch blade construction comprising, incombination, a sheet metal switch blade, means defining a circularopening through said switch blade and a collar of metal formed from themetal of said switch blade surrounding said circular opening, said metalcollar being shaped so that the circular edge in the switch blade, whichwould normally surround said opening, is disposed in a plane spaced fromand substantially parallel. to the plane of the main portion of saidswitch blade, and an elongated ceramic pin being force lit through thecircular opening in said switch blade and being in frictional grippingengagement with a circumferential portion of the inner surface of saidmetal collar, to effect a permanent resilient gripping of said ceramicpin by the material of said collar without effecting structural failureof the material of said collar.

2. A bimetal-operated switch blade construction comprising, incombination, a sheet metal switch blade, means defining a circularopening through said switch blade and a collar of metal formed from themetal of said switch blade surrounding said circular opening, said metalcollar being shaped so that the circular edge in the switch blade, whichwould normally surround said opening, is disposed in a plane spaced fromand substantially parallel to the plane of the main portion of saidswitch blade, and an elongated ceramic pin being force fit through thecircular opening in said switch blade and being in frictional grippingengagement with a circumferential portion of the inner surface of saidmetal collar, to effect a permanent resilient gripping of said ceramicpin by the material of said collar, and the terminus of said collarbeing spaced from said switch blade a distance of from 2 to 4 times thethickness of the material of said switch blade.

3. A bimetal-operated switch blade construction comprising, incombination, a sheet metal switch blade, means defining a circularopening through said switch blade and a collar of metal formed from themetal of said switch blade surrounding said circular opening, said metalcollar eing shaped so that the circular edge in the switch blade, whichwould normally surround said opening, is disposed in a plane spaced fromand substantially parallel to the plane of the main portion of saidswitch blade, and an elongated ceramic pin being force fit through thecircular opening in said switch blade and being in frictional grippingengagement with a circumferential portion of the inner surface of saidmetal collar, to effect a permanent resilient gripping of said ceramicpin by the material of said collar, and the terminus of said collarbeing spaced from said switch blade a distance in the range of 3 timesthe thickness of the material of said switch blade.

4. A bimetal-operated switch blade construction com prising, incombination, a sheet metal switch blade, means defining a circularopening through said switch blade and a collar of metal formed from themetal of said switch blade surrounding said circular opening, said metalcollar being shaped so that the circular edge in the switch blade, whichwould normally surround said opening, is disposed in a plane spaced fromand substantially parallel to the plane of the main portion of saidswitch blade, and an elongated ceramic pin being force fit through thecircular opening in said switch blade and being in frictional grippingengagement with a circumferential portion of the inner surface of saidmetal collar, to effect a permanent resilient gripping of said ceramicpin by the material of said collar, and the axial length of said collarbeing selected to effect sufiicient compressive action between thecollar and the ceramic pin to hold the ceramic pin firmly in positionand to provide sufficient area of contact between the collar and ceramicpin to distribute said compressive force on the ceramic pin to preventcompression-failure of the ceramic.

References Cited in the file of this patent UNITED STATES PATENTS2,008,163 Walder July 16, 1935 2,502,291 Taylor Mar. 28, 1950 2,785,278Peterson Mar. 12, 1957

